Rake is the angle between the headset tube and a vertical line. Increasing
the rake will move the front tire farther from the bike. Rake is measured
in degrees, and is a frame specification. To visualize trail, draw an
imaginary line along the path of the headset tube to the ground. Measure
from this point to the center of the tire patch. This is trail, and is
measured in inches.

The amount of rake is significant in determining a motorcycle's handling
characteristics. In general, more rake provides greater straight line
stability, less rake makes the bike more responsive. Larger values of
trail also create more straight line stability. This is why the forks
on a sportbike are more vertical than those of a cruiser.

Visualize the wheels of a shopping cart for an illustration of a machine
with zero rake and a lot of trail. Exciting handling, but zero straight
line stability.

People frequently inquire about using so called "raked trees",
which don't actually affect rake at all, rake is built into the steering
head angle, but rather it offsets the front axle and cosmetically gives
the forks a raked look while reducing trail. For a good illustration and
explanation of rake and trail, how to measure it and figure out whether
you're going to get yourself in trouble, check out the
Swedish side below (for the Metrically Inclined)

Here's a handy Rake and Trail Calculator. The illustration shows two neck
rake angles to illustrate raked trees. They probably did this because the
drawing would be even more confusing if they drew a second set of forks,
a wheel moved forward with the axle moved forward (as is the case with trees
that have positive offset). This should help settle arguments about how
much "rake" or angle offset in trees is acceptable before handling
becomes a dangerous issue. Just enter the numbers in the calculator and
your question is answered.

Explanations aside, the calculator appears to work great, but I'd still
"measure twice and cut once" with a ruler and protractor: